This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To compare the protective capabilities of four broadly neutralizing monoclonal antibodies. This project includes four main experiments: EXPERIMENT 1: In this experiment we compared the antiviral efficacy of two broadly neutralizing monoclonal anti-HIV antibodies: clone 2F5 and 4E10. 16 animals were included in this experiment (6 animals per monoclonal antibody and 2 animals for the control group treated with indifferent antibody, and 2 animals for viral stock control without any antibody treatment). The 12 study animals received 50mg/kg 2F5 or 50mg/kg 4E10 antibody intravenously 24 hours prior to the viral challenge. The control animals received indifferent IgG1 antibody. To maintain the desired antibody level we repeated the antibody administration 1 day after the viral challenge. Viral challenge was performed on all treated and control animals by administering 2000 TCID50 SHIVBAL intrarectally. We have completed this experiment and found that with the exception of the control animals all of the macaques (12 animals) were protected against the viral challenge. We decided to test the longevity of the protection by challenging the animals again without further antibody administration. We used the same route and viral stock for challenge (2000 TCID50 SHIVBAL intrarectally). Concurrently we challenged 2 na[unreadable]ve animals to assess the quality of the virus stock. After we have completed the rechallenge we found that with the exception of one animal all the macaques became persistently viremic. We rechallenged the remaining one animal to test whether there was still existing protection in the SHIV exposed, but aviremic animal. After this third challenge the animal became persistently viremic. EXPERIMENT 2: In this experiment we studied whether the monoclonal antibody 2G12 is more effective in vivo than predicted by its in vitro neutralization activity. 9 female animals were included in this experiment (5 animals for the 2G12 antibody treated group, 2 animals for the control group treated with indifferent antibody, and 2 animals for viral stock control without any antibody treatment). Prior to the antibody administration each animal received 30 mg Depo Provera i.m. in order to thin the vaginal epithelium and make the animals more susceptible to the viral challenge. To decrease possible preexisting genital tract inflammation that may affect the viral transmission we put the animals on a 7-day course of Baytril (Enrofloxacin) at a dose of 2.5 mg/kg BID (twice a day). This antibiotic regimen is in accordance to clinically prescribed regimens by the veterinarians of the Primate Center. 24 hours before viral challenge the animals were treated with 40mg/kg 2G12 antibody intravenously. Viral challenge was performed on all treated and control animals by administering 500 TCID50 SHIV162P3 intravaginally. We have completed this experiment. The results show that of the 5 2G12 antibody treated animals 2 were completely protected, 1 animal showed signs of transient viremia and 2 animals became permanently viremic. EXPERIMENT 3: In this experiment we determined whether different, intravenously administered HIV neutralizing antibodies were secreted at the same level into the vaginal cavity. 12 female animals were included in this experiment (4 animals received b12 HIV neutralizing antibody, 4 animals received 2G12 neutralizing antibody and 4 animals received LALA b12 antibody). We have included only four animals per group since the purpose of the experiment is to collect initial data. We have completed this experiment and the obtained data were included in a successful R-01 grant proposal. EXPERIMENT 4: In this experiment we will determine whether an intravaginally administered HIV neutralizing antibody (SIgA b12) will protect the animals against intravaginal SHIV162P3 challenge. 12 female animals will be included in this experiment (5 animals will receive 5 mg SIgA b12 HIV neutralizing antibody, 5 animals will receive 0.2 mg SIgA b12 HIV neutralizing antibody and 2 animals will receive an isotypic control, non-neutralizing antibody). We have included only five animals per group since the purpose of the experiment is to collect initial data. If we find robust differences between the effective neutralizing concentration of the antibody we may decide to increase the number of participating animals. This experiment is in the scheduling phase. We plan to perform it by 2009-03-31.